I recently experienced a problem with the distributor gear of a 1989 Mustang. It wears out on one side of the gear - like 3 to 4 sections of the gear. We replaced the camshaft using a new high performance one and also replaced the gear with an Iron one ( supposedly stronger ) and once we started the engine, the same thing happened to the distributor gear. Since we installed a high vol oil pump, we were advised that that could be the problem. We went back to a regular new oil pump, an iron rod for the pump and another distributor gear and the car ran for only 5 minutes before smashing one side of the distributor gear again. Any suggestions?
Are you using the cast iron distributor gears? If so, these cannot be used with roller camshafts, which is what I assume your '89 5.0 has.
The cast iron works with a flat tappet cam, but you MUST use a hardened steel or bronze gear with a roller cam. Hope that helps.